Getting started with Box2D in Flash is harder then it should be. The demos are great and if you spend some time with them and the Box2D forums you can get up and running pretty quick. It’s a shame there isn’t more tutorials yet. I hope this intro will help get people started a bit quicker. I will post more as I do more with it.
Units in the Box2D examples seem strange at first until you find out the secret. They are use the units from the C++ package which measured things in meters. They are making a meter = 30px in flash. If you just change the m_drawScale of the debug draw to 1 everything will be in pixels
Everything in Box2D is setup with a centered registration point. SetAsBox() through me off at first because I was expecting it to take the full width and height of the box as parameters but it actually takes half the width and height. See diagram below.